As Nadir said, we pray the angelus standing. However according to the Raccolta it is to be prayed kneeling except on Sunday. Like the rosary, we prefer to do the same every day instead of what is asked of us.
Partial excerpt from the 1887 Raccolta.
75. THE "ANGELUS DOMINI," ETC., OR THE "REGINA COELI," ETC.
The seraphic Doctor St. Bonaventura, in the General Chapter of his Order, held at Pisa in the year 1262, directed his religious to exhort the faithful to say, at the sound of the church-bell at even, three times the Ave Maria, in veneration of the mystery of the Incarnation of the Son of God in the most pure womb of the Blessed Virgin, by the operation of the Holy Ghost. This same devotion, which bad been already introduced in the episcopal church of Saintes (the capital of Saintonge in Western France), was approved by Pope John XXII., by a bull dated from Avignon, Oct. 13, 1318, who granted several days of Indulgence to all who should practise it with contrition; and this grant was renewed by him, May 7, 1327, in the injunction he sent to his Cardinal Vicar, to give at even in Rome a signal, by the sounding of the church-bell, to remind all persons to say these three Ave Maria's. See F. Theodore a Spiritu Sancto, de Indulgentiis, part ii. art. iv. § v.
In later times Pope Benedict XIII. opened the treasury of the Church to bestow greater Indulgences in furtherance of this pious practice; being desirous that all the faithful, not once only but many times a day, should implore the protection of the Ever-blessed Virgin, and venerate the grand mystery of the Incarnation. Accordingly, by a universal Brief, Injuncta nobis, of Sept. 14, 1724, he granted to all Christians who, at the sound of the bell, morning, noon, and even, at sunset, shall say on their knees daily the Angelus Domini, &c., with three Ave Marias, -
Afterwards Pope Benedict XIV., by a formal notice issued by his Cardinal-Vicar, published in the year 1742, April 20, confirmed the above-named Indulgences, at the same time declaring that the Angelus Domini was to be said standing, every Sunday in the year, beginning from first Vespers, that is, Saturday evening; and that in Paschal tide the Regina coeli, should be said in its stead, always standing, with its proper V., R., and prayer.